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From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Wed, 04 Sep 2024 07:41:38 -0700
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References: <vaq762$1ssg1$1@solani.org> <vb163a$1dt9b$1@dont-email.me> <0ns8djtqe7ct4k21h8ubnj944fonq9i0u0@4ax.com> <vb29rd$1isoo$1@dont-email.me> <l4h9djl9rg8qip36cq0luehvf8cqprklbt@4ax.com> <orh9dj1svvp2i1rnhbkt3266uovqotofi4@4ax.com> <bmn9djt23ns3akfnfjaltiehr3ccuotkcs@4ax.com> <6p8adjh4ief0cfk1ohc1i54t6tob41q6o6@4ax.com> <nbgbdjtdf30hje01rqq5v0tptvpkknikbn@4ax.com> <vb4le6$2t5h0$1@dont-email.me> <pjccdjlu3d9glr745kpbsq9u6a6dqa28r0@4ax.com> <vb5edf$3100v$1@dont-email.me>
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On Mon, 2 Sep 2024 22:32:15 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>john larkin <jlarkin_highland_tech> wrote:
>> On Mon, 2 Sep 2024 15:25:59 -0000 (UTC), Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> 
>>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>>> On Sun, 01 Sep 2024 19:49:39 -0700, john larkin
>>>> <jlarkin_highland_tech> wrote:
>>>> 
>>>>> On Sun, 01 Sep 2024 17:43:32 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>> wrote:
>>>>> 
>>>>>> On Sun, 01 Sep 2024 13:17:03 -0700, john larkin
>>>>>> <jlarkin_highland_tech> wrote:
>>>>>> 
>>>>>>> On Sun, 01 Sep 2024 15:53:46 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>>>> wrote:
>>>>>>> 
>>>>>>>> On Sun, 1 Sep 2024 17:55:58 -0000 (UTC), Phil Hobbs
>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>> 
>>>>>>>>> john larkin <jlarkin_highland_tech> wrote:
>>>>>>>>>> On Sun, 1 Sep 2024 17:45:46 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>>>>>>>> wrote:
>>>>>>>>>> 
>>>>>>>>>>> On 30/08/2024 2:21 am, Jan Panteltje wrote:
>>>>>>>>>>>> On a sunny day (Fri, 30 Aug 2024 00:43:39 +1000) it happened Bill Sloman
>>>>>>>>>>>> <bill.sloman@ieee.org> wrote in <vaq1f2$jdj$1@dont-email.me>:
>>>>>>>>>>>> 
>>>>>>>>>>>>> It's lot easier and quicker to bread-board a circuit in LTSpice than it
>>>>>>>>>>>>> is to wire up a test circuit, but what that means is that you need to
>>>>>>>>>>>>> make fewer real circuits and they are a lot more likely to work when tested.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> That, on it's own, is enough to explain why labs look different today
>>>>>>>>>>>>> than they did in the dark ages.
>>>>>>>>>>>> 
>>>>>>>>>>>> All it explains is boeings falling apart and astronuts ending up stuck at the ISS
>>>>>>>>>>>> and no moonlanding from the US, not even a probe.
>>>>>>>>>>>> Slimulations are _not_ realty and never will be.
>>>>>>>>>>> 
>>>>>>>>>>> But they can capture useful parts of reality, if you know what you are 
>>>>>>>>>>> doing.
>>>>>>>>>>> 
>>>>>>>>>>> John Larkin's simulated inductors tend not to have any parallel capacitance.
>>>>>>>>>> 
>>>>>>>>>> The trick is to know when it matters. ESR and core loss are usually
>>>>>>>>>> more important.
>>>>>>>>>> 
>>>>>>>>>> I designed this surface-mount inductor for my Pockels Cell driver,
>>>>>>>>>> after several tries using commercial parts. They all smoked.
>>>>>>>>>> 
>>>>>>>>>> It's wound on a specially marked Sharpie pen that we have carefully
>>>>>>>>>> reserved.
>>>>>>>>> 
>>>>>>>>> It better have a regular calibration schedule, or your semiconductor
>>>>>>>>> customers may give you the raised eyebrow. 
>>>>>>>> 
>>>>>>>> Hmm.  To be overly serious:  With traceability to NIST (US) or NPL
>>>>>>>> (UK) or the like.
>>>>>>>> 
>>>>>>>> The trend in standards is to eliminate standards tied to a physical
>>>>>>>> object.
>>>>>>>> 
>>>>>>>> I have a Sharpie in hand.  The barrel that is not covered by the cap
>>>>>>>> is a truncated cone, being 11.0 mm at the blunt end and 12.32 mm near
>>>>>>>> the cap, 73 mm away.
>>>>>>> 
>>>>>>> Mine is pretty cylindrical for the length of the coil. I expect that
>>>>>>> the operator's (ie, my)  applied tension affects the radius too.
>>>>>> 
>>>>>> Most likely.
>>>>>> 
>>>>>> 
>>>>>>> That inductor sees 25 amps p-p, roughly a sawtooth, at 4 MHz. The
>>>>>>> Coilcraft parts that I tried all smoked, I guess from skin effect and
>>>>>>> proximity effect.
>>>>>>> 
>>>>>>>> 
>>>>>>>> Actually, all that's needed is to specify an ideal geometric shape,
>>>>>>>> with tolerances, in the formal documentation.  
>>>>>>>> 
>>>>>>>> Joe Gwinn
>>>>>>> 
>>>>>>> I'll have someone start on a SolidWorks model.
>>>>>> 
>>>>>> I bet you need the standoff, so the lossy FR4 material isn't too
>>>>>> close.  That should be in the requirements as well.
>>>>> 
>>>>> The turns squish down into the gap-pad gunk, which is an OK heat
>>>>> conductor. The PCB under the pad is a big copper pour, top and bottom,
>>>>> with a zillion thermal vias.  There's more gap-pad on the underside of
>>>>> the board to dump heat into the baseplate.
>>>>> 
>>>>> At 4 MHz, skin depth is 32 microns, so most of the copper is wasted.
>>>>> That's why it gets so hot.
>>>>> 
>>>>> I tried three of the Coilcraft 1010VS parts in series, but they
>>>>> smoked, probably skin+proximity effect.  Maybe parallel would have
>>>>> been better.
>>>>> 
>>>>>> 
>>>>>> I'd specify the coil dimensions, not the mandrel dimensions, which may
>>>>>> be provided as a helpful suggestion only.
>>>>>> 
>>>>>> Joe Gwinn
>>>>> 
>>>>> I could have a mandrel machined or 3D printed, to more accurately wind
>>>>> the inductor. The improvement would be mostly cosmetic.
>>>> 
>>>> Or choose a 12mm OD mandrel, and adjust elsewhere.  The advantage of
>>>> 12mm is that it's a common size. so just buy the rod and use it.
>>>> 
>>>> .<https://www.mcmaster.com/products/shafts/shafts-2~/rotary-shafts-5/diameter~12-mm/>
>>>> 
>>>> Actually, the requirement is a certain inductance while handling a
>>>> 4-MHz sawtooth at 25 Amps (p-p), so the frequency band is roughly 4 to
>>>> 20 MHz, to cover the first five harmonics  Which harmonic causes the
>>>> most heating?
>>>> 
>>>> The dimensions et al are the construction details needed for Highland
>>>> to be able to replicate the part without your help.
>>>> 
>>> Lo these forty year gone, I had this RF gig that involved making a lot of
>>> VHF LC oscillatior and filter protos. 
>> 
>> I still design LC oscillators!
>> 
>>> 
>>> We had a hand-cranked coil winder that had a good selection of cylindrical
>>> steel mandrels with helical grooves to guide the wire, plus three or four
>>> sheets with tables of measured values for single-layer coils of various
>>> lengths.  With a couple of training runs, one learned how hard to pull on
>>> the wire so that it would just spring free from the mandrel. 
>>> 
>>> That made it easy to make nice looking, high-Q coils for the inductance
>>> range of interest.  Good Medicine. 
>>> 
>>> Cheers 
>>> 
>>> Phil Hobbs 
>> 
>> Coilcraft makes a bunch of bare-naked RF inductors.
>> 
>> We like this encapsulated part:
>> 
>> https://www.coilcraft.com/en-us/products/rf/air-core-inductors/midi-spring/1812sms/?skuId=26054|26274
>> 
>> What's surprising is that the "natural" tempco of a copper solenoid
>> inductor runs around +120 ppm/degC, but this one is around +40. The
>> plastic must compensate for the copper somehow.
>> 
>> 
>> 
>> 
>
>Sounds awfully high. 
>
>To about 1% accuracy (over most useful aspect ratios), the inductance of a
>single-layer coil is 
>
>L(uH) = a**2 n**2 /(9a + 10b), 
>
>Where a is the mean radius and b is the overall length, both in inches. 
>
>If the thermal expansion is unconstrained, a and b vary together, so the TC
>of inductance of such a coil is the same as the CTE of copper, about 17
>ppm/K. 
>
>A solid plastic form is strong enough to stretch the copper and increase
>the TCL to the CTE of the plastic. 
>
>If the length only is constant, the TCL is increased, and for a short fat
>coil it’s nearly doubled. 
>
>In the case of something like B&W Miniductor, which has fairly fine-pitched
>turns held by a few small axial stringers, the plastic stretches the length
>of the coil but leaves the radial expansion free. 
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